Perimeter of Triangle

Perimeter of Triangle: The Perimeter of any two-dimensional figure is defined as the distance around the figure. We can just calculate the perimeter of any closed shape just adding up the length of each of the sides. In this article will first learn about what is perimeter, how to find the perimeter of different types of triangles when all side lengths are known. At last solved examples help you get more clarification on the topic.

What is the Perimeter of a Triangle?

The sum of the lengths of the sides is the perimeter of any polygon. In the case of a triangle,

Perimeter = Sum of the three sides.

Always include units in the final answer. If the sides of the triangle are measured in centimeters then finals answer should also be in centimeters.

Perimeter of Triangle Formula

The formula for the perimeter of a closed shape figure is usually equal to the length of the outer line of the figure. Therefore, in the case of a triangle, the perimeter will be the sum of all the three sides. If a triangle has three sides a, b and c, then,

Perimeter, P = a + b +c

Perimeter of a Isosceles, Equilateral and Scalene Triangle

Below table helps us to understand how to find the perimeter of different triangles- Equilateral triangle, Isosceles triangle and Scalene triangle.

Equilateral Triangle

Isosceles Triangle

Scalene Triangle

P = 3.I

P = 2.I + b

P = a + b + c

Perimeter of a Equilateral Triangle
Perimeter of a Isosceles Triangle
Perimeter of a Scalene Triangle

Where a, b, c and l are the side lengths, and P = Perimeter.

This formula implies to find the perimeter of a triangle, add the lengths of all of its 3 sides together. If A, B and C are the side measures, and X is perimeter then

Perimeter Of Triangle

Perimeter of Right Triangle

A right triangle has a base(b), hypotenuse(h) and perpendicular(p) as its sides, By the pythagoras theorem, we know,

h2 = b2 + p2

Therefore, the Perimeter of a right angle triangle= b + p + h

Perimeter of right triangle


Let us consider some of the examples on perimeter of a triangle:

Example 1: Find the perimeter of a polygon whose sides are 5 cm, 4 cm and 2 cm?

Solution: Let,

a = 5 cm

b = 4 cm

c = 2 cm

Perimeter = Sum of all sides = a + b + c = 5 + 4 + 2 = 11

Therefore, the answer is 11 cm.

Example 2: Find the perimeter of a triangle whose each side is 10 cm.

Solution: Since all three sides are equal in length, is an equilateral triangle.

Perimeter = 30 cm. Answer!

Example 3: What is missing side length of a triangle whose perimeter is 40 cm and two sides are 10 cm each.

Solution: Given,

Perimeter = 40 cm

Length of two sides are same i.e. 10 cm, is an isosceles triangle.

Using formula: P = 2l + b

40 = 2 * 10 + b

40 = 20 + b

or b = 20

Missing side length is 20 cm.

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